It is known to treat fibers of tobacco smoke filters with acid components in order to adsorb basic constituents of the tobacco smoke. Thus DE-C 1,300,854 describes the treatment of the filter fibers with acid esters of organic polycarboxylic acids, such as citric acid, tartaric acid, succinic acid, malic acid and sugar acids, for this purpose. These acid esters can be finely divided on the fibers together with glycerol triacetate. DE-C 1,051,182 relates to the treatment of filter fibers based on cellulose with alginic acid and pectic acid. Finally, DE-A 1,956,949 describes the impregnation of filter fibers with tartaric acid.
In general, the previously known processes suffer from the disadvantage that the solvents and/or hardeners, such as glycerol triacetate (triacetin), which are customary in the preparation of filters in the cigarette industry are poor solvents of dicarboxylic or polycarboxylic acids. The process of the invention is aimed at the elimination of this disadvantage.